1. Field of the Invention
The present invention relates to the use of coextruded sealing ribs on zipper flanges to enhance the quality of the sealing between the flanges and the walls of a reclosable package. The present invention further relates to placing grip strips on the opposite side of the flanges from the ribs in order to improve the quality of the sealing even further.
2. Description of the Prior Art
Most currently manufactured flexible packaging is constructed from films including polypropylene. However, the application or sealing of reclosable zippers to polypropylene has been problematic at best. In general, polypropylene is minimally compatible with the polyethylene-based sealant materials that are typically found on a reclosable zipper. The resulting bond strengths between the polyethylene flange and the polypropylene film are typically not as strong as can be expected in polyethylene laminate packaging, and the temperatures required to form these weak bonds are very near to the temperatures which induce distortions in the film.
While forming zippers from polypropylene can result in stronger bonding between the zipper flanges and the film, these zippers are typically stiff and less flexible than polyethylene zippers, and therefore not as desirable.
Moreover, in thick film, gusseted, transverse direction package constructions, the zipper is prone to inner flange sealing due to the small sealing window of this zipper film combination. Similarly, when the slider zipper is notched, zipper transport can be problematic as the notches create sections of zipper that are more prone to deformation due to drag or tension transients.